https://stackoverflow.com/questions/44918368/return-type-with-generic-with-bounds

gistfile1.txt

Welcome to Scala 2.11.8 (OpenJDK 64-Bit Server VM, Java 1.8.0_131).
Type in expressions for evaluation. Or try :help.

scala> :paste
// Entering paste mode (ctrl-D to finish)

import scala.concurrent.Future
import scala.concurrent.ExecutionContext.Implicits.global

class RequestType {}
case object Read extends RequestType
case object Write extends RequestType

def dbrequest[T <: RequestType](d: T): Future[T] = {
    d match {
        case Read => println("reading"); Future(d)
        case Write => println("writing"); Future(d)
    }
}

// Exiting paste mode, now interpreting.

import scala.concurrent.Future
import scala.concurrent.ExecutionContext.Implicits.global
defined class RequestType
defined object Read
defined object Write
dbrequest: [T <: RequestType](d: T)scala.concurrent.Future[T]

scala> dbrequest(Read)
reading
res0: scala.concurrent.Future[Read.type] = Success(Read)

scala> dbrequest(Write)
writing
res1: scala.concurrent.Future[Write.type] = Success(Write)